Heat-treating furnace



Dec. 11, 1928. 1,694,964

- H. o. BREAKER HEAT TREAT ING FURNACE Original Filed Feb. 27, 1924 Patented Dec. 11, 1928.-

Y UNITED STATES HARRY O. BREAKER, OF BUFFALO, NEW YORK.

HEAT-TREATING FURNACE;

Application filed February 27, 1924, Serial No. 695,451. Renewed June 14, 1927.

This invention relates to furnaces for heat treating metal parts, and more especially to electric furnaces designed for this purpose. The invention is particularly concerned with 5 the control of the atmosphere within the fur- It is frequently desirable to heat treat metal parts in an inert or non-oxidizing atmosphere for the purpose of preventing the scaling of the parts. This is particularly true when the parts under treatment have been partially or wholly machined since it permits the passing of the parts on to the next operation in a clean condition and eliminates any necessity for removing the scale. In some cases, also, it is necessary to carry on the heat treat:

ment in an atmosphere of reducing gas or in' a gas of some special composition.

The present invention deals with the problems presented by these conditions, and it aims to devise ,a furnace construction in which the gas within the furnace can be readily controlled, andin which the interchange of the gas in the furnace with the surrounding atmosphere shall be reduced to a minimum. It is also an object of the invention to devise an apparatus of this character which can be manufactured economically, will be convenient to use, and will have a high thermal efficiency. 3

In a prior application I have disclosed a furnace in which these objects are realized to a very satisfactory degree, and it is a further ob]ect of this invention to improve and per-v fect the furnace shown in my earlier application, with a view particularly to controlling evenmore accurately the atmosphere which comes in contact with the metal parts during their treatment. 3

The nature of the invention will'be readily understood from the following description when read in connection with the accompanyiing drawing, and the novel features will be particularly pointed out in the appended claims.

The single figure of the accompanying drawing is a vertical, cross sectional View of a furnace structure embodying the present invention, some of the parts appearing in elevation and some being indicated diagrammat ically. I

The construction shown comprises an elec trio furnace having side walls 2 and a top 3, these parts being made of any suitable materials and supported in a structural steel shell in the usual manner. It will be understood that these parts usually comprise a lining of vitreous brick, or other fire resistant material, backed by suitable heat insulating materials. In constructing this portion of the furnace the standard practice may be followed except that no openings are made other than those that may be required for observation purposes, and these are normally-closed. Also,

the walls and shell of the furnace should be made as gas tight as possible. Metallic resistors, indicated at 4, are secured to the side walls 2 and are connected with suitable sources of current to supply the necessary degree of heat to the furnace. The furnace is supported in an elevated position by means of structural steel members, indicated in general at 5, which rest on a suitable floor 6.

The hearth 7 of the furnace is mounted on, or forms part of, a bottom 8 which, in the present instance, is supported on a car, the frame or body of which is shown at 9, the wheels being indicated at 10. For the purpose of raising the bottom 8 of the furnace and the hearth 7 into their operative positions, as shown in the drawings, and lowering them out of said positions again to facilitate loading and unloading, these parts are mounted on the platform 12 of an elevator. Preferably the elevator is of the hydraulic type, including a plunger 13 and piston 14. The piston works in a cylinder 15 to which water or other fluid under pressure is sup plied, as desired, by the pump 16. A pit 17 is formed in the floor 6 to receive the platform 12. In order to lock the'car in its elevated position and permit the platform to be lowered, four stops are provided, two of is secured to and surrounds the margin or outer edge of the bottom 8. v This trough cohtains sand or some other sealing material into which the edge of the plate 28 is forced; so that as the furnace bottom ismoved into its no i tom 8 an of the operative osition, the space between the botd the side walls 2 is automatically sealed. The furnace thus forms an enclosure adapted to confine an atmosphere or body of gas and to substantiall prevent interchange of this atmosphere wit 1 the surrounding atmosphere.

Located closely adjacent to the furnace is a gas holder comprising a tank 36 and a bell 38 telescoping within the tank. This holder is supported on a bracket 37 and it is connected with the upper part of the furnace by a pipe 35. The lower edge of the bell is sealed by a suitable liquid, such as a heavy mineral oil. A lever 39 connected to the bell and having aweight 40 adjustable thereon almost counter balances the bell so that it exerts only a. slight pressure on the gas stored therein.

In using this furnace the oxygen contained in the air within the furnace becomes burned out-very quickly and the gases remaining are inert, or at least, non-oxidizing. When the bottom of the furnace is lowered for the unloading and loading operations, the hot air or gas in the furnace remains pocketed therein due'to the fact that the onl opening in the furnace is at its bottom. onsequently, there is practically no tendency for this heated, burned out atmosphere to interchange with the. surrounding: atmosphere. Any such tendenc further .is reduced by the use as ho der. That is, when the bottom of the urnace is lifted into its operative position to introduce a new charge into the furnace and current is turned on to the resistors,

the resulting increase in temperature expands the atmosphere within the furnace and part of this atmosphere is forced into the bell 38. After the heat treating operation has been completed and the current is turned off to allow the charge 'to cool, the as pressure within the furnace falls and t e gas previously forced out of the furnace is returned to the furnace again by the bell 38. Substantially the same atmosphere, therefore, is retained in the furnace and the gas holder al most indefinitely so that when the 0 gen has once been burned'out of this atmosp ere, the remaining gases are held within the furnace and the gas holder substantially without change during the treatment of successive charges. This is a very important practical advantage in preventing the scaling of metal parts 1 during the heat treatment. It is of further advantage, also, in improving the thermal efficiency of the furnace since the walls of the furnace cannot give up their heat to the sur-- rounding atmosphere asthey do in furnaces of the ordinary construction where a free circul'atron of cold air-1s permitted through the furnace whenever it is opened. This arrange- }ment, also, is of advantage when a gas or gases. other than the atmospheric gases, are

have so far that the invention may be embodied in other opened and the charge removed. When such an arrangement is employed, the gas bell automatically supplies inert gas to the furnace as the cooling operation progresses.

While I have herein shown and described the best embodiment of my invention that I devised, itwill be appreciated forms without departing from the spirit or scope thereof.

Having thus described my invention, what I desire to claim as new is 1. An apparatus of the character described,

comprising, in combination, an electric furnace lncluding fixed top and side walls and a removable bottom, an elevator for raising said bottom into its cooperative relationship to the other parts of the furnace and for lowering' it out ofsaid relationship, and'means connected With said furnace for receiving gas displacedfrom the furnace and for subsequent-1y returning said gas again to the furnace.

2. An apparatus of the character described, comprising, in combination, an electric furnace including fixed top and side walls and a removable bottom, an elevator for raising said bottom into its cooperative relationship to the other parts of the furnace and for lowerin it out of said relationship, and a gas hol er communicating with said furnace, said holder enclosure for retaining a given body of gas substantially without interchange with the surrounding atmosphere. 1 v

3. An apparatus of the character described, comprising, in combination,an'electric furnace including fixed top and side walls and a removable bottom, an elevator for raising said bottom into its cooperative relationship to the other parts of the ble gas holder, and, a pipe connecting the interior of said furnace with whereby gas forced outof the furnace upon an increase in pressure therein will subse-- and furnace cooperating to form an furnace and for low- 'ering it out of said relationship, an expansisaid gas holder,

comprising, in combination, an electric furliquid in said tank, a counter balance for nace includmg fixed top and Side walls and a said bell, and plpe connections between said removable bottom, an elevator for raising bell and the upper part of said furnace persaid bottom into its cooperative relationship mitting a free flow of as in either direction to the other parts of the furnace and for lowbetween said bell and urnace. ering it out of said relationship, a gas bell, a tank in which saidibell is mounted, a sealing HARRY O. BREAKER. 

